THE GEOCHEMISTRY OF DOMESTIC SPRING WATERS, SOUTHERN ETHIOPIA: CRITICAL INFORMATION FOR SPRING HEAD WATER SOURCE PROTECTION

Less than 15 % of the rural population of the Southern Region in Ethiopia has potable water and much of this population uses contaminated streams, puddles, and shallow wells. HOPE International has capped many low yield springs (> 0.2 L/s) in Ethiopian highlands to protect the water resource and route water to villages in the valleys We report the results of a geochemical study of the water quality of over 50 of capped and uncapped springs along a topographical gradient in the Lake Chamo and Lake Abaya Drainage Basin from ~1100 to 3000 m.a.s.l. The purpose of this study was to determine if concentrations of major solutes, nutrients and the ä18O and äD of water could be used to characterize the water source and the extent to which contamination has occurred. One subset of springs, mostly capped, had dilute water with chemical composition similar to that of precipitation in contrast to deeper groundwater that have base cation concentrations commensurate with reactions of precipitation with minerals associated with the volcanic rift rocks. These dilute spring waters probably discharge from short local flow systems. The local meteoric water line derived from the isotopic content of the dilute spring waters is ~äD = 8.1ä18O + 19.0. The isotopic variability of the spring waters mostly are related to local elevation effects. All spring waters are potable, but some have concentrations of total dissolved nitrogen > 6 mg/L (as N) and phosphate > 0.2 mg/L (as PO4) caused by local agricultural contamination up-gradient of the affected springs. HOPE has initiated a spring-head protection program including planting thorn bushes, to inhibit livestock from entering local spring recharge zones. Inexpensive field kits to measure nutrient concentrations may be a key to spring-head protection in this remote region.